1. Field of the Invention
The invention relates to communications circuitry, and particularly to communications circuitry for combining a terrestrial signal and a satellite signal into an integrated digital signal for delivery to users.
2. Description of the Prior Art
Communication systems provide various broadband services such as telephone, television, and Internet to subscriber""s homes. These services are typically provided by either an exchange of a satellite signal with a satellite system, or an exchange of a terrestrial signal with a terrestrial communications system.
Satellite systems are well suited for broadcast services, such as audio and video programming, but are not well suited for mass full duplex communications like voice telephony and two-way data services. Satellite systems suffer from problems, such as latency or delay of signal transmission, that effect the quality of service necessary for telephony and real time data services. Terrestrial communications systems on the other hand, are designed for full duplex communications offering little or no delay for services such as voice telephony, data streaming multimedia, and other real time sensitive communications.
One example of a satellite system is a Direct Broadcast Satellite (DBS) system illustrated in FIG. 1. DBS is a digital satellite system that broadcasts television signals received by a relatively small and inexpensive satellite dish antenna typically mounted on either the roof or side of a house. DBS transmissions have enormous capacity, with each satellite having 16 transponders that operate in the KU-band spectrum at fairly high power levels. Using data compression and multiplexing, a pair of satellites working together have the potential to provide over 150 conventional non-high definition television video and audio channels via 32 transponders.
The KU band is the portion of the electromagnetic spectrum in the 12 Ghz to 14 Ghz range. DBS satellites typically employ 14 Ghz on the uplink to the satellite and 12.2 to 12.7 Ghz on the downlink to the dish antennas. The dish antennas receive DBS signals containing original picture and sound information and provide those signals to a DBS receiver connected to the subscriber""s television. A low-noise block converter (LNB) converts the 12.2 to 12.7 Ghz downlink signal from the DBS satellite into a 950 to 1450 Mhz signal required by the DBS receiver. A tuner in the DBS receiver isolates a single digitally modulated 24 Mhz transponder, while a demodulator converts the modulated data into a digital data signal for output over the subscriber""s television.
Two types of LNBs are available: dual and single output. Single-output LNBs have one radio frequency (RF) connector while dual-output LNBs have two. The dual-output LNB can be used to feed a second receiver or other form of distribution system. Both types of LNBs can receive both left and right-hand polarized signals. Polarization is selected electrically with a direct current (DC) voltage fed onto the center connector and shield of the coax cable from the receiver. The right-hand polarization mode is selected with +13 volts while the left-hand polarization mode is selected with +17 volts.
Audio and video signals from the program provider are encoded and converted to data packets. The configurations can vary, depending on the type of programming. The data packets are then multiplexed into serial data and sent to a transmitter. To minimize the data-transfer rate, the data is compressed using Motion Picture Expert Group (MPEG2), a specification for transportation of moving images over communication data networks. Compression is accomplished by predicting motion that occurs from one frame of video to another and transmitting motion data and background information. By coding only the motion and background difference, instead of the entire frame of video information, the effective video data rate can be reduced from hundreds of Mbps to an average of 3 to 6 Mbps. This data rate is dynamic and will change, depending on the amount of motion occurring in the video picture.
In addition to MPEG video compression, MPEG audio compression is also used to reduce the audio data rate. Audio compression is accomplished by eliminating soft sounds that are near the loud sounds in the frequency domain. The compressed audio data rate can vary from 56 Kbps on mono signals to 384 Kbps on stereo signals.
To prevent unauthorized signal reception the video signal is encrypted or scrambled at the uplink site. A secure encryption xe2x80x9calgorithmxe2x80x9d Digital Encryption Standard (DES) is used to encode the video information. The keys for decoding the data are transmitted in the data packets. A customer Access Card decrypts the keys, which allows the receiver to decode the data.
Referring to FIG. 2, the video program information is completely digital and is transmitted in data xe2x80x9cpackets.xe2x80x9d Examples of data packets are Video, Audio, Conditional Access (CA), compatible serial data, and Program Guide. The video and audio packets contain the visual and audio information of the program. The CA packet contains information that is addressed to each individual receiver. This includes customer e-mail, Access Card activation information, and which channels the receiver is authorized to decode. The Program Guide maps the channel numbers to transponders and also gives television program listing information.
Each data packet contains 147 bytes. The first two bytes of information are contained in the Service Channel ID (SCID). The SCID is a unique 12-bit number from 0 to 4095 that uniquely identifies the packet""s data channel. The Flags consist of 4-bit numbers, used primarily to control whether or not the packet is encrypted and which key to use. The third byte of information is made up of a 4-bit Packet-Type indicator and a 4-bit Continuity Counter. The Packet Type identifies the packet as one of four data types. When combined with the SCID, the Packet Type determines how the packet is to be used. The Continuity Counter increments once for each Packet Type and SCID. The next 127 bytes of information consists of the xe2x80x9cpayloadxe2x80x9d data, which is the actual usable information sent from the program provider.
Unfortunately, DBS systems only provide national television programming and not local television programming. Local programming reception requires switching to a conventional antenna and use of a different infrared remote controller. When local programming is desired, the user operates a switch in the receiver to invoke connection of the outside antenna for local broadcast reception.
Terrestrial communications systems on the other hand, provide a wide range of services including local television programming and real time full duplex communications. Terrestrial communications systems are increasing in bandwidth through technologies such as asymmetrical digital subscriber lines (ADSL), very high speed subscriber lines (VDSL), Cable Modems and Broadband Wireless Systems. These systems employ physical wireline and wireless transmission mediums, such as twisted pair, fiber, coax, microwave, free space laser, and use transport layer and service layer protocols such as Asynchronous Transfer Multiplexing (ATM), Transmission Control Protocol/Internet Protocol (TCP/IP), and Time Division Multiplexing/Time Division Multiple Access (TDM/TDMA).
Some examples of terrestrial communications systems include but are not limited to, broadband wireless systems which operate at microwave frequencies of 1 Ghz-38 Ghz, VDSL systems, ADSL systems, and optical systems which operate at wavelengths such as 1550 NM. One example of terrestrial broadband wireless system is a microwave multi-point distribution service (MMDS) system. MMDS was originally an alternative to cable-based cable television, but is now authorized for two-way or one-way communications of telephony voice, data, and video. MMDS can also carry signals compatible with a DBS system having similar compression, digital packet format, data encryption, synchronization, programming authorization and billing processes. The microwaves employed by the MMDS band are electromagnetic waves in the radio frequency spectrum between 2.15 to 2.162 Ghz and between 2.5 to 2.690 Ghz.
The present invention advances the art by providing communications circuitry that integrates a satellite signal and a terrestrial signal to optimize the ability of user devices to process these signals. Integration of satellite signals and terrestrial signals also provides enhanced service offerings. Broadband terrestrial network properties, such as full-duplex, high speed, low latency, and high capacity, complement the broadcast program capacity of satellite systems. Integration of broadband terrestrial networks and satellite systems enables a robust and broad array of telephony, data, national and local broadcast, as well as on demand video programming.
The present communications circuitry comprises integration circuitry coupled to interface circuitry. The integration circuitry is configured to convert at least a portion of a terrestrial signal into a satellite channel frequency and to combine the converted terrestrial signal and a satellite signal into an integrated digital signal. The terrestrial signal occupies at least one unoccupied channel in the satellite signal. The interface circuitry is configured to provide the terrestrial signal and the satellite signal to the integration circuitry and to transmit the integrated digital signal.